sub2ind is not giving me diesired results

Hi how can you find linear indices of a certain rectangular region in an image. I have its x,y width and height i also have image width and height. Sub2ind is not working or perhaps i dont know how to achieve it using sub2ind. I only want linear indices of a 23x51 area. My X cordinat is 237 and Y is 228 and image size is 375,500. So if provide something like this

 linearInd = sub2ind([23 51], 237, 228);
obviously it prompts error that out of range subscript

Thanks

Answer 1

[Guillaume]

The first argument to sub2ind is the size of your whole image, not the region you want to extract. The second and third arguments would be the coordinates of the image you want to convert to indices. One way to do what you want:

img = randi([0 255], 512, 512); %random 256x256 image for demo
x = 237, y = 228, width = 51, height = 23;

[xx, yy] = meshgrid(x:x+width-1, y:y+height-1);
indices = sub2ind(size(img), yy, xx);

I have to ask, though, why do you want to convert to linear indices?

[Lora]

It workss thanks. The reason why i am trying to extract is that have ground truth objects in linear indices nd it would be easier to compute overlap.

Answer 2

[Azzi Abdelmalek]

You have a problem with the size of your matrix, if your matrix is 23x51 how can you get the coordinates [237 228]?

[Lora]

yes I know but my question is how can i get linear indices of a just a rectangular region of an image of size(375,500) now the size of my rectangular region is 23x51? but my rectangular region start from (237,228)